Often there is a need to reduce the transmission of vibration between two elements of an engineering structure while still maintaining mechanical support. The ultimate aim can be associated with reducing the effects of vibration and/or noise on both people and equipment.
One such problem is the reduction of broadband cabin noise within civil aircraft. This is conventionally achieved by improving the soundproofing within the cabin (which normally entails a consequent increase in weight), together with the use of simple passive isolators to reduce vibration transmission between the main air frame and the interior trim panels. The latter is important because the vibration path through the trim panel mounts is the dominant one in many cases e.g. for excitation by the external turbulent boundary layer pressure field. The reason for this is that the boundary layer pressure field generally produces subsonic vibrations and thus transmission between the air frame and the trim panel through the air insulation gap is normally small compared to the transmission through the mechanical couplings.
Current practice is to use small blocks of elastomeric material for the isolation. Such isolators reduce vibration transmission above the resonant frequency associated with the isolators' stiffness reacting against the receiving mass: the so-called isolation frequency. The use of an elastomer provides sufficient internal damping so that the classical increase in transmission at the isolation frequency is small.
However, an elastomer does not behave as a classical stiffness isolator because its stiffness increases with increasing frequency. This can produce a much higher transmission than the classical spring at frequencies well above the isolation frequency. Also, elastomers are notoriously temperature sensitive which can compromise the performance.
The problem with replacing the elastomeric material with a member that has a classical spring stiffness behaviour is that high vibration transmission will occur at and around the resonance frequency associated with the isolator's stiffness against the receiving mass. Unfortunately, introducing large amounts of damping into such a spring arrangement such as a metal spring in order to reduce the vibration transmission at or around the resonance frequency is difficult when a long service life is required. Additionally, the use of heavy damping produces unwanted increases in transmission either side of the isolation frequency.
It is therefore an object of the present invention to provide an improved vibration isolation mount and method.